The invention relates to a safety valve.
A typical safety valve includes a body which defines a chamber into which two fluid conduits run. The flow of the fluid through the conduits is controlled by the valve. A sleeve houses a spring which biases a clapper towards a seat. A passage is thus provided between the chamber and one of the conduits.
Generally, the clapper has two opposite faces, an extreme face, which is displaced to obstruct the passage, and a rear face, which is biased by an elastic resilient member, such as a spring, against a thrust-stop, which is associated with the sleeve. The characteristics of the spring, along with the distance provided between the thrust-stop and the clapper's rear face, determine the "tear-off" pressure of the clapper, the pressure at which the clapper is torn from its seat.
Use of a thrust-stop to support the elastic member has been disclosed in French Patent No. A-2-528.526. The thrust-stop includes a centrally located basin-like cap in which the elastic member is located. A mechanical part in the shape of a skirt is joined to the rim of the cap. The skirt rises concentrically in relation to the cap. Its free end is anchored in a bore, the anchoring being on the level of a groove and precluding any withdrawal from the thrust-stop. As a consequence, the tear-off spring cannot be replaced. However, an adjustment of the tear-off pressure may be made by changing the penetration distance of the thrust-stop in the bore, e.g., by increasing the penetration distance. The thrust-stop may be threaded into the bore.
Safety valves also generally include a servicing and handling assembly connected with the clapper, including a handling rod by which the clapper can be raised. The flow circuit can thus be closed "upstream."
Means are associated with the sleeve of the valve body that cooperate with the handling assembly to enable the voluntary handling operation. In concentrational valves, the clapper is mechanically dependent on the foot of the handling rod. When mounting and dismounting, the handling assembly is connected with the handling rod so that the handling assembly can be removed from the handling rod. Thus, the supporting thrust-stop of the spring can be reached more easily.
The displacement of the clapper between its open and closed positions is guided by the handling rod. The guidance is generally accomplished by a supplementary member means which closes the sleeve, and by means which cooperate with those of the handling assembly. This supplementary member, which is usually on the body of the valve, can easily be removed. The clapper has an obstruction head which is at too great a distance from the clapper to adequately guide it. As a result, further means are required to provide guidance.
To protect the parts housed in the sleeve from damage by the fluid, and/or to assure flow without excess turbulence, a closing membrane is generally associated with the clapper at the entrance of the corresponding sleeve. The membrane is secured in an air-tight manner and is imperviously fixed around the periphery of the sleeve.
As these valves are currently designed, their tear-off pressure is adjustable by screwing and unscrewing the thrust-stop. An incorrect adjustment can hinder normal service of the valve, jeopardizing safety and potentially causing serious damage.
Accordingly, it is an object of the invention to provide a valve wherein the tear-off pressure cannot be changed. A further object of the invention is to reduce the number of parts, and to achieve a feasible, simplified safety valve apparatus at an affordable price.